Dear Dr. Anselm,
Thanks four your help,
Best regards!
nafiva
On Thu, Nov 10, 2016 at 6:21 PM, Dr. Anselm Horn <anselm.horn.fau.de> wrote:
> Dear asdda asa,
>
> > Can we compute RESP charges on compound which geometry-optimized on the
> > 3-21G* basis set of the Hartree-Fock?
>
> short answer: yes.
>
> long answer:
> Atomic charges per se are a quantum chemical construct, there are no
> "correct" charges. In MD simulations, atomic charges are used to model
> the electrostatic interaction between atoms.
> In Amber, these charges are derived following a rather standardized
> protocol, e.g. RESP charges from a HF/6-31G(*) electron density of one
> or more structures for ff99SB or FF14SB.
> (cf F.-Y. Dupradeau's tools http://q4md-forcefieldtools.org/FyD/ )
>
> However, the choice of the right structure(s) is up to you; often one
> would use a QM geometry optimization at the same level as the RESP
> charge derivation, but a different approach is also possible. Thus, you
> may obtain "reasonable" charges from a 6-31G(*) electron density
> computed for your 3-21G* optimized geometry; but if it is
> computationally feasible, I'd suggest a re-optimization of your
> structure with the larger 6-31G(*) basis set.
>
> Regards,
>
> Anselm
>
>
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Received on Thu Nov 10 2016 - 14:30:03 PST
